EXT-6937 PARTIAL FIXED Enable a possibility to "mute everyone" in case group...

EXT-6937 PARTIAL FIXED Enable a possibility to "mute everyone" in case group chat is already in "moderate_mode" state.

Partial fix (until restart moderator's viewer)
* store "moderate_mode" session state
* if session is already in requested state participants un/mute individually.

Known Issue:
"moderate_mode" session state is set to false on startup. Thus if moderator join voice chat with disabled voice it has incorrect state.
In this case when he sends "Mute everyone" request first time it has effect only to himself. Other unmuted participants are not muted.
Next "Mute everyone" request works properly: one request per participant is sent.

Reviewed by Aimee Walton at https://codereview.productengine.com/secondlife/r/423/

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branch : product-engine